The present invention relates to a video camera and, more particularly, to a video camera that can perform enlargement of dynamic range of such as a video movie, successive picturing of frame still images, and enlargement of dynamic range of frame still images.
As a method for enlarging the dynamic range of a video camera, there is a method which is described in Japanese Published Patent Application No. Hei 6-13207. In this method, a first exposure signal such as a long term exposure signal (hereinafter, xe2x80x9cSlong signalxe2x80x9d) and a second exposure signal such as a short term exposure signal (hereinafter, xe2x80x9cSshort signalxe2x80x9d) are synthesized, thereby enlarging the dynamic range on appearance.
This method will be briefly described with reference to the drawings.
FIG. 17 is a block diagram illustrating an example of construction of a prior art video camera 6. FIG. 18 is a diagram schematically showing the storage state and transferring state of Slong signals and Sshort signals which are light-electricity converted by a progressive scanning CCD 11 in the prior art video camera.
This video camera 6 is constituted by a taking lens 10, a progressive scanning CCD 11, a switch 12, a signal synthesizing means 18, and a camera signal processing part 20.
In addition, the progressive scanning CCD 11 is constituted by light-electricity conversion parts 50, vertical transfer parts 52 transferring charges in the vertical direction, which charges are transferred from the light-electricity conversion parts 50, a horizontal transfer part 54 which outputs serially in the horizontal direction the charges which are transferred from the vertical transfer parts 52, and an output amplifier 56 which amplifies output of the horizontal transfer part 54.
The light-electricity conversion part 50 comprises photodiodes 51, the number of which corresponds to the pixel number, and the vertical transfer part 52 comprises a plurality of CCD 53 which are respectively vertically arranged respectively corresponding to the photodiode 51.
While in FIG. 18 an array which has 4 rows of pixels and 6 columns of pixels is illustrated, in an actual construction of such as VGA (Video Graphics Array), a construction which has 640 rows of pixels and 480 columns of pixels is adopted.
In the video camera 6 constructed as above, the light incident to the video camera through the taking lens 10 is light-electricity converted in the progressive scanning CCD 11.
In other words, in this progressive scanning CCD 11, as shown in FIG. 19, in the period of one field, i.e., the vertical scanning period (hereinafter also referred to as xe2x80x9c1Vxe2x80x9d), the exposure time is switched between the long exposure time T1xe2x80x2 and the short exposure time T2xe2x80x2 by means of an electronic shutter (not shown here) so that the exposure amount against the light-electricity conversion part 50 in the progressive scanning CCD 11 may be different.
Here, T1xe2x80x2 is set to about {fraction (1/60)} second, and T2xe2x80x2 is set to about {fraction (1/1000)} second. Video images of one screen are respectively imaged during T1xe2x80x2 and T2xe2x80x2, thereby outputting a signal to the vertical transfer part 52 at the timing shown in FIG. 19. The signal read out during T1xe2x80x2 becomes a Slong signal and the signal read out during T2xe2x80x2 becomes a Sshort signal.
The Slong signals and the Sshort signals which are obtained with light-electricity converted by the respective photodiodes 51 of the light-electricity conversion part 50 are read out to the vertical transfer part 52 as shown by arrows in the figure so that outputs from the upper and lower photodiodes 51 which are adjacent each other are added respectively, in a vertical blanking period (in this case during T1xe2x80x2-T2xe2x80x2). Therefore, in the vertical transfer part 52, the Slong signal and the Sshort signal are respectively stored at the position of CCD 53 designated by a black circle and at the position of CCD 53 designated by a white circle, alternatingly.
Therefore, the respective Slong signal and Sshort signal stored in the vertical transfer part 52 are transferred alternatingly to the horizontal transfer part 54 by line by line, and thereby they are output from the light-electricity conversion part 50 through the output amplifier 56. Accordingly, when, for example, the progressive scanning CCD 11 comprises 480 pixels in the vertical direction, Slong signals of 240 lines and Sshort signals of 240 lines are respectively output from the light-electricity conversion part 50 in the period of one field, i.e., 1V.
After the Slong signal and the Sshort signal, which are serially output line by line from the progressive scanning CCD 11, are separated into the Slong signal and the Sshort signal by the switch 12, these signals are synthesized in the signal synthesizing means 18 to be output to the camera signal processing part 20 as a signal of one series. Accordingly, in the case of non-interlacing system, the above example results in synthesized signals of 240 lines (hereinafter, xe2x80x9cSmix signalxe2x80x9d) in the period of one field, i.e., 1V.
Here, while as shown in FIG. 20 the above Slong signal is saturated at the light incident amount of L1xe2x80x2 due to the large exposure amount, this Slong signal has a large change of signal level at the light incident amount below that, thereby resulting in a preferred S/N ratio and keeps the gradation at the low luminescent part.
On the other hand, while the Sshort signal has low gradation at the low luminescent part due to the low exposure amount, it keeps the gradation without saturating up to the high luminescent part on the contrary. Therefore, the gradation characteristics of the Smix signal, which has synthesized the both, is enlarged relative to the gradation characteristics of the Slong signal only, and thus, the dynamic range on appearance is enlarged.
In this way, the Smix signal whose dynamic range is thus enlarged by the signal synthesizing means 18 is processed to a video signal which is adaptive to the television display (such as NTSC system) by the camera signal processing means 20, and is output to the outside.
However, the above-described prior art video camera 6 has the following problems.
First of all, since in the prior art video camera 6 T1xe2x80x2 is set to {fraction (1/60)} sec. and T2xe2x80x2 is set to {fraction (1/1000)} sec. as described above, the enlargement rate (xcex81xe2x80x2/xcex8sxe2x80x2) of dynamic range in this case is about 16 times [≈({fraction (1/60)})/({fraction (1/1000)})].
However, when T2xe2x80x2 is quite a short time, such as when T2xe2x80x2 is {fraction (1/1000)} sec., not only the S/N ratio of the Sshort signal itself is insufficient but also the gradation of the video image imaged by the video camera 6 becomes insufficient as well.
In other words, in case where such enlargement rate of dynamic range amounts to about 16, and when the scenery inside the room and that outside as shown in FIG. 21 are imaged together, while the video images of the clear part 72 (scenery outside) and of the dark part 71 (inside the room) are obtained as clear ones, the video images of the intermediate part 73 (periphery of a window, such as a desk adjacent to the window) for which the enlargement rate of dynamic range of about 2xcx9c4 times is made the most appropriate cannot be made clear images due to the too large enlargement rate of dynamic range in the prior art device, thereby resulting in a large problem.
With reference to FIG. 20, this problem is explained as a fact that when the light incident amount is within a range of L1xe2x80x2 to L2xe2x80x2, since the signal level of the Sshort signal at that timing is low while the Slong signal is saturated, the S/N ratio is deteriorated, whereby the Smix signal is affected by noise components to result in non-preferred video images.
In the above-described prior art video camera 6, when the progressive scanning CCD 11 is used for enlargement of dynamic range, it is not possible to accomplish the inherent object as the progressive scanning CCD 11 itself, i.e., to obtain the progressive scanning output, particularly, the output that has enhanced the picture quality by vertical high frequency emphasizing.
More particularly, though in the above-described video camera 6 it is intended that Slong signals of 240 lines and Sshort signals of 240 lines are respectively output from the progressive scanning CCD 11 in the period of one field, the both signals are synthesized by the signal synthesizing means 18, resulting in only Smix signals of 240 lines. Therefore, it was not possible to utilize the video camera in case where high quality video image of 480 lines should be printed out by non-interlacing system, for example.
It is an object of the present invention to provide a video camera in which the practical enlargement rate of dynamic range, such as two times to four times, can be obtained, and further the progressive scanning CCD can be used for the enlargement of dynamic range and progressive scanning output.
To solve the above problem, a video camera comprising a progressive scanning CCD, a driving means for driving the progressive scanning CCD, and a camera signal processing part for converting an output of the progressive scanning CCD to a video signal adaptive to a video image display, and enabling enlarging dynamic range by synthesizing a first signal which is obtained by exposure during a first predetermined time and a second signal which is obtained by exposure during a predetermined time after the exposure time of the first signal, by means of the progressive scanning CCD and enlarging luminance gradation characteristics on appearance, which further comprises a separating means for separating the first signal and the second signal which are output from the progressive scanning CCD at different timings, a signal synthesizing means for synthesizing the first signal and the second signal to produce a synthesized signal, and a delay means for receiving the first signal output from the separating means and delaying the first signal by a predetermined time so that the second signal and the first signal are simultaneously input to the signal synthesizing means.
A video camera comprising a progressive scanning CCD, and a camera signal processing part for converting an output from the progressive scanning CCD to a video signal adaptive to video image display, and enabling enlarging dynamic range by synthesizing a first signal which is obtained by exposure during a first predetermined time and a second signal which is obtained by exposure during a second predetermined time after the exposure time of the first signal, by means of the progressive scanning CCD to enlarge luminance gradation characteristics on appearance, which further comprises the progressive scanning CCD enabling outputting the first signal and the second signal at different timings, a signal separating switch for separating the first signal and the second signal which are output from the progressive scanning CCD, a delay means for delaying an output from the signal separating switch by one horizontal scanning period, a first memory for temporarily storing an output from the delay means, a second memory for temporarily storing the second signal which is output from the signal separating switch, a first scanning conversion means for converting an output from the first memory to a normal speed signal, a second scanning conversion means for converting an output from the second memory to a normal speed signal, and a synthesizing means for synthesizing the first signal and the second signal, synchronized and having normal speeds, which are output from the first scanning conversion means and the second scanning conversion means.